In recent years, as image processing and computer graphics technologies have developed, there has been increasing demand for the display of a cross-sectional image of a three-dimensional image in real-time. Such real-time image display is used, for example, when a presentation is given to a customer to display a building before, during and after construction or an automobile during the design phase, and when an explanation is given to a patient and his/her family by displaying the body of the patient in a medical clinic. The “cross-sectional image” used herein includes an image showing a cross section of a three-dimensional image by cutting the three-dimensional image along a cross-sectional cutting plane, a perspective image of the three-dimensional image when the cross-sectional cutting plane is set internally or externally to the three-dimensional image, and the combination of the perspective image and the image showing the cross section.
Patent Document 1 discloses an example of conventional art that may be applied to meet such demands, being an apparatus for drawing a cross-sectional view taken along a cutting line drawn in a plan view. The apparatus includes a storage unit for storing plan view information representing the plan view. The plan view information is read from the storage unit and the plan view is drawn based on the read plan view information. Then, the cross-sectional view is drawn based on intersection information regarding the intersections of the cutting line and other lines in the plan view and on height information regarding the height.
In this technology, by using the above plan view as the plan view of the three-dimensional image of the building, automobile, or patient's body described above and displaying the thus drawn cross-sectional view as an image, cross-sectional views of the three-dimensional images of these objects can be displayed.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2001-52038